Xmas job: Fix the RTC on Party Zone - Help!

[shansta]

Like the subject says - am going to have a go at this one over the break...

I got 2 weeks with my little darlings - think it might be time to work on the pinnys... 

Electronically - I know enough to be dangerous would be the best way to put it...

1991 WPC-DMD - Party Zone

My RTC is stuck where I set it to (Time & Date), More of an issue is that the GI lighting is NOT going into power save mode.

What I understand is that this is generated by a circuit on the CPU board - which feeds 32Khz into pin 32 of U9.

I think the oscillator circuit is running (Pins 54-57) as the game works fine? If that's dead the game wouldn't boot, would it?

1. Does this sound correct?

2. I don't have a CRO (Wouldn't know how to drive it!)

3. I do have a fluke meter and a logic probe (shitty one from Jaycar).

I found the leg broken off the crystal and re-soldered that - it has continuity to the back of the board.

Anything I can probe/test to see what to start replacing?

Turf the 3 caps? (C28-30). BTW - what does "22P" and "100P" mean in uF?

Killed the crystal by soldering the leg?

Any thoughts, ideas etc. etc.

Shane.

[Marty Machine]

Just about all RTC chips require a 32.768khz crystal for timing reference.
The 2 small caps are definately required and some of the chips are a little fussy about the value of the caps.

I wouldn't think these parts would go faulty, other than being broken on the board by mishandling etc.

What's the number of the RTC chip? if we dig up a data sheet, we may find there's a few pins that provide other timing signals which are measurable with a probe/meter. (1 pulse-per-second output is a typical signal).

I guess the next step is to determine which pin(s) carry the data to the main CPU, and confirm thsoe tracks aren't broken anywhere, maybe a dodgy connector?

Are the volts to the chip ok? 5V stable etc etc?

MM.

[shansta]

Looking at my copy of the schematic - U21 is a MC14584BCP.

Uses pin 13 input from the crystal, 12 out to pin 70 of the custom chip (This should be the 32khz clock signal? Marked 32khz on the diagram), pin 14 Vcc which measures 4.48v with the board removed and not powered on. I have checked continuity between the parts of the circuit - all checks okay - no corrosion up there? Bearing in mind I am an an idiot.

This thing has has corrosion repaired in the past (looks like a good job too) - U18,19&20 all socketed and the remote battery mod. Wrong end of the board though?

The only thing with the RTC circuit was the xtal which had come adrift? (It now has continuity to both sides of the board)

[Steevsee]

BTW - what does "22P" and "100P" mean in uF?

I think the 'P' refers to Picofarad.
Here is a conversion table. http://www.justradios.com/uFnFpF.html

[shansta]

Thanks Steve!

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Don't know about my logic probe... Pulse light stays on whenever it's hooked up to 5v? (I am using the TP on the driver board) I thought the LED's would stay off until you probe a chip...

I get nothing on either pin 12 or 13 of the RTC chip (Stays low) - the probe is working as I can see pulses on various other chips.

[Marty Machine]

If you try your probe on EVERY pin of that Chip, there should be some pulsing on at least 1 pin....
If not, the Crystal (or chip?) has died.

edit : the MC14584BCP is just a cmos hex schmidt trigger IC, not a timeclock IC.
I'd say that chip (with crystal) is the main 32khz oscillator feeding elsewhere.

Is your crystal the tiny cylinder shape? about 3mm wide by 10mm long?
I have a bunch of them, if you want me to bring one to the meet this Saturday?

MM.

[shansta]

According to the schematic - pins 12,13,14 are connected - the rest are unused?

Hang on I'll blow up the bit I am talking about...

And yes I will grab a crystal off you please. (It's the round one like you said)

[Marty Machine]

Yep, just as i imagined.....what chip is that 32khz signl going into?

[shansta]

Ahh sorry - it's the ASIC chip.